The concept of the item is that for each time a champions movement is impaired for a short duration (say 5 seconds), the champion gains significant tenacity increases to a point where he can no longer be disabled for a shorter duration (let’s say 2 seconds). After this effect, the item goes on cooldown and the champions tenacity returns to its normal levels. Make the item purely HP, don’t tie it to MR or Armor (this would make it blatantly unfair against one class). Give it some regen or some other generic stat (anything but CDR) to make it a little more appealing, but make the cost entirely based around its passive.
This would significantly reduce the effectiveness of brainless chain cc spam, and it being purely HP with no offensive stats would make it appealing to bruisers and maybe even tanks.